Systemic sclerosis/scleroderma is a chronic autoimmune disease of unknown etiology, characterized by altered cell-mediated immunity, in the production of autoantibodies, and the excessive deposition of collagen in viscerae and skin. Human disease is difficult to study because the early changes are subtle and diagnosis is often delayed, and existing murine models for scleroderma are limited in their usefulness for study of the complex immunologic abnormalities. Evidence from in vitro and in vivo work on pulmonary lesions in human scleroderma suggests that TGFbeta1 produced by activated monocytes in dermal perivascular compartments is a potent stimulus for collagen gene up-regulation by fibroblasts, leading to fibrosis. Hypothesis: cutaneous monocyte activation in dermal perivascular compartments and differentiation to TGFbeta1-producing cells are critical events in early scleroderma. In am studying these events in two murine sclerodermatous graft-versus-host disease (GVHD) models [(C57BL/6J to LP/J) and (B10.D2 to Balb/c)] in which animals develop GVHD, skin thickening and autoantibodies after bone marrow transplantation across minor histocompatibility loci. Control mice receiving the reciprocal bone marrow transplantation (LP/6 to C/57BL/6J) develop GVHD and dermal mononuclear cell infiltrates, but do not develop the skin thickening. Aim I: To determine the sequence of early critical events in the dermal microvascular compartment in skin of animals with sclerodermatous GVHD in order to better understand the pathophysiology for sclerodermatous disease, and to devise novel focused interventions. In situ hybridization and immunostaining studies to establish the time course of activation of endothelium, influx of monocytes, and production of TGFbeta1 will provide a foundation for focused in vivo interventions. Aim II: To employ in vivo interventions testing involvement of specific cytokines (TGFbeta1) and cell types (monocyte/macrophages) in sclerodermatous disease. Can the sclerotic process be inhibited using monocyte/macrophage-directed therapy? Infusion of antibodies against monocyte surface molecules (Mac-1, LFA-1, VLA-4) and products (TGFbeta1) by miniosmotic pumps in vivo provides a system in which variables can be manipulated to test the hypothesis that monocyte TGFbeta1 production is critical to initiation and progression of fibrosis. Identifying major early immunologic events in scleroderma will provide a means to test innovative immunotherapies in vivo.